Weed and grass trimmers using flexible cutting lines are in widespread use. Many of these trimmers employ a rotatable hub with a short length of nylon or copolymer nylon or other plastic line extending from the hub. When the hub is rotated, the tip of the line extending from the hub provides the cutting or trimming action. Grass and weed trimmers using this principle of operation have been popular for their versatility of use and because the flexible trim line is safer to use than rigid rotating steel blades.
Various types of trimmer devices have been developed for using such flexible trim lines. Typically, rotating line trimmers or string trimmers employ a line having a generally circular cross section. This line, in many trimmers, is wound on a storage reel in the hub of the device, and is played out of a hole in the hub in discrete amounts as the line breaks off or wears off. When the supply of line on the storage reel in the hub is used up, additional line is provided from a continuous length of line supplied as replacement line in a trimmer line package. The line which is provided in such packages typically is equal to the amount of line wound on a storage reel of the hub of a trimmer device, or it is in excess of the amount of line which can be wound on a hub, thereby providing more than one set of line replacements.
Generally, the trimmer line which is used in rotating string trimmers is manufactured or extruded of monofilament nylon or copolymer nylon material. The cross-sectional diameters of the line used in the trimmers vary from larger cross-sectional diameters for commercial trimmers to smaller diameters in the trimmers sold for intermittent home use. Even though different diameter line sizes are employed, the range of sizes is relatively narrow (typically, 0.050" to 0.155" in diameter). Trimmer lines which have cross sections other than circular cross sections have been developed in an attempt to provide sharper cutting edges at the point of impact when cutting grass or weeds. Cross-sectional configurations in the form of elongated ribbed lines, or a star-like cross section, or square, or triangular cross sections have been developed. The overall cross-sectional dimension, however, still is within the range given above for typical circular lines.
The packaging of low-cost replacement lines for string trimmer devices typically has been in the form of blister packages on printed paperboard stock. Some packaging operations use folded plastic blister packages or what is known as "clam packs" as an alternative. These folded blister packages are sealed by locking ridges or tabs, which are formed on the two halves of the package.
Originally, the loops or coils of string trimmer line, typically ranging in length from 25' to 50', were wound and then taped or restrained with twist ties or other fastening devices. The taped or restrained coil of trimmer line then was placed in the blister cup; and the cup then was closed (in the case of the folded blister packages) or the cup was sealed to the paperboard backing stock. This method of first coiling the line, then restraining it and placing it into the package proved to be costly to manufacture. In addition, it was less desirable for the end user, since the line had to be completely removed from the package and then either the taped twist tie or other restraining device had to be removed in order to use the line.
For the packaging in the form of blister packages on printed paperboard stock, the flat stock forming the base of the package may be considered as a four-layer sandwich. The base layer is the paperboard stock itself. Then, a thin clay coating is placed over this layer to facilitate the printing of various indicia on the clay coating applied to the stock. After the printing ink has been applied to form the package identification colors and instructions, a thin plastic coating is applied over the printing. The coil of line is placed in the pre-formed PVC blister cup or container, for containing a fixed length coil of trimmer line, then the filled cup is placed on the flat board stock; and heat and pressure is used to seal an outwardly extending flange on the blister to the plastic coated paperboard backing material. Typically, the blister is a cup having circular cross sections. This cup is open on the side which is attached to or sealed to the paperboard backing.
Subsequently, techniques for placing a spiral coiled line inside a package were developed. This provided a lower-cost package, and one that allowed for dispensing the line from the coil without destroying the package. Such products have been supplied for many years. The clamshell blister, however, did not lend itself well to such a dispensing package, particularly for larger sizes of the coiled trimmer line, since the separating force of the coiled line caused the package to open.
Such packaging, however, has been used in the combination of the blister and paperboard package combination. A hole is first formed through the paperboard backing at approximately the center of this cup. Next, trimmer line is wound through the hole in an appropriate length by an automatic or semi-automatic winding machine to fill the blister cup with a desired length of trimmer line after the cup has been sealed to the backing board. The end of the trimmer line then is extended through the hole in the backing; so that it can be withdrawn in a desired amount and cut to length.
The packaging which has been described immediately above is used by many manufacturers of extruded trimmer line for packaging and displaying replacement line for sale. A problem which arises in the use of such packages, however, is that during shipping, handling, storage and display for sale of such trimmer lines, particularly in relatively high humidity climates, the packages open through separation of the flange on the blister pack from one or more of the layers of the paperboard backing. When this occurs, the line in the package then falls out or is exposed; and the damaged package cannot be sold. Efforts to solve the problem of separation of the backing from the blister have not been successful. Part of the reason is that the backing cards generally are manufactured by one manufacturer, the blister is thermoformed by another manufacturer, and the sealing equipment, made by still another manufacturer, is used by the customer packaging the string trimmer line. Each of these parties tends to assign responsibility for the problem to one of the other parties.
The problems may be found in several areas. With respect to the card, separation can result from improper coating, the age of the cards, humidity and temperature. With respect to the blister pack, silicone release on the sealing side may result in an improper seal being effected. Also, forming of the blister at too low a temperature may lead to residual stress in the formed part. The blister, upon sealing, will shrink and this may lead to separation from the card. For the sealing machines, uneven pressure and uneven heat or non-calibrated temperature and pressure control may result in an improper bond being formed. Finally, with respect to the customer assembly to produce the finished package, using the wrong temperature or not enough seal time, or not enough pressure in the use of the sealing machine, also may result in failure of packages.
It is desirable to provide a package particularly suited for packaging coils of replacement string trimmer line which overcomes the disadvantages and problems of the prior art in a simple and effective manner.